1. Field of the Invention
This invention pertains to balancing devices, and more particularly to apparatus for balancing rotating bodies having variable mass centers.
2. Description of the Prior Art
The constant quest for higher productivity and greater accuracy poses difficult problems for many manufacturing industries. The challenges of designing and building equipment capable of efficiently and accurately producing round parts extends to machine tools wherein a contouring head machines a stationary workpiece. An exemplary contouring machine is the Numeribore.TM. machine manufactured by the Davis Tool Division of AMCA International Corporation.
Because of the high speeds demanded of modern contouring machines, the contouring heads must be accurately balanced. Unbalanced conditions result in inaccurate geometries. When cutting varying bore sizes or other tapered surfaces of revolution with contouring heads, the changing distance of the cutting tool and tool slide from the axis of rotation requires the application of a correspondingly changing counterbalance force.
The balancing problem is aggravated when contouring is performed by relatively small heads. In many cases, the small envelope required for the contouring head to machine specific workpieces makes it very difficult to provide sufficient mass to properly counterbalance the cutting tool and slide. The problem is especially acute in contouring heads having relatively large slide travels and high rotational speeds.
Attempts have been made to solve the foregoing problems. For example, U.S. Pat. No. 4,577,535 describes a contouring machine tool having a counterbalanced contouring head. A pair of counterweights are geared inside the contouring head to move radially to the axis of rotation in the opposite direction as the cutting tool and slide. While generally satisfactory, the system of the U.S. Pat. No. 4,577,535 has a maximum operating speed that is somewhat lower than desired. U.S. Pat. No. 4,620,464 discloses a counterbalanced boring head, but the tool travel available is very limited. Other known counterbalance systems are also unable to satisfactorily compensate for variations in the positions of the radially moveable parts and variations in the weights of the radially movable parts of high speed contouring heads.